1. Field of the Invention
This invention relates to dishwasher tubs, and particularly to a new and improved plastic dishwasher tub assembly of one piece homogeneous construction comprising a plastic front-loading tub, a plastic multirib frame about the opening in the tub, and a plastic box-like base section, which combination of elements provides both ease of construction and proper structural support.
2. Description of the Prior Art
Plastic dishwasher tubs are in use in large capacity front-loading dishwashers of the type normally comprising upper and lower dish-supporting racks and a front swing-down door. Dishwashers of this type are disclosed in U.S. Pat. Nos. 3,811,746 and 3,826,553 assigned to the same assignee as the present invention.
The advantages of using a one-piece plastic dishwasher tub rather than a metal tub are numerous. For example, cost factors are greatly decreased in the manufacture of a molded plastic tub as compared to those involved in the manufacture of a metal tub, which requires an inner coating or lining operation. Other advantages include a reduction in finishing labor requirements, particularly tub welding operations, a longer tub life due to corrosion resistance which is independent of faulty coating procedures or chipping, and a decrease in thermal and acoustical transmission which minimizes the need for separate heat and sound insulation.
However, plastic tubs tend to deform. Deformation may occur when the tub is subjected to the high normal operating temperatures in a dishwasher, such as to approximately 180.degree. F. Deformation may also occur when the tub is subjected to various loading forces, such as the weight of the dishwasher itself when placed on an uneven floor. Such deformation is undesirable and must be prevented for several reasons. More specifically, and in order for the swing-down door on a front-loading dishwasher to maintain a proper water seal to prevent leakage, the original cross-sectional rectangular shape of the tub must be maintained. Dish racks must be free to slide in and out of the dishwasher, an action which would be inhibited by tub deformation. Further, a tub which deforms under heat or load forces lacks an appearance or "feel" of quality.
The most commonly used means for preventing plastic tub deformation is the use of a metallic base and a metallic supporting collar placed around the tub. Although these measures effectively eliminate deformation, the use of metal members as a collar and base involves many of the same disadvantages which prompted change-over from metal to plastic tubs. These include not only corrosion related problems, but also the labor time required to mount the collar and base on the tub. Additionally, metallic parts must be manufactured separately from the plastic tubs and thus production and shipping costs are increased. Further, openings must be cut in metal bases in order to provide access to dishwasher components located underneath the tub, a step which requires even further labor time and cost.
The primary object of the present invention is to provide a new and improved plastic tub assembly including means for preventing deformation and thus maintaining the rectangular cross-section of such tubs.
Another object of the present invention is to eliminate the problem of corrosion inherent in a dishwasher tub assembly when metallic parts are used therein to maintain rigidity.
Another object of the present invention is to provide a one-piece plastic dishwasher tub assembly which eliminates the labor step of assembling the base and frame structure to the tub separately.
Still another object of the present invention is to provide a plastic dishwasher tub assembly with cutouts premolded into the base for allowing access to dishwasher components underneath the tub, and thus obviating the need for additional labor steps to provide such cutouts.